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Ge 116 Module 1: Scanning Electron Microscopy

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Presentation on theme: "Ge 116 Module 1: Scanning Electron Microscopy"— Presentation transcript:

1 Ge 116 Module 1: Scanning Electron Microscopy
Part 2: EDS X-ray analysis and EBSD

2 Continuum X-rays

3 Characteristic X-rays

4 Characteristic X-rays

5 Characteristic X-rays

6 X-ray counting: EDS and WDS

7 X-ray counting: EDS and WDS
Spectral resolution determined by electron-hole pair production energy and thermal noise

8 X-ray counting: EDS and WDS
Silicon Drift Detector (SDD) – new! Low capacitance allows MUCH higher counting rate Reaches optimal resolution at higher temperature (LN2 not required!)

9 X-ray counting: EDS and WDS
Rise time of steps depends on capacitance of system, limits counting rate. Conventional Si detector is periodically discharged. SDD is continuously discharged (less dead time).

10 Energy-Dispersive X-ray Spectrum

11 Complexities in X-ray production
Production, (z) Pure Cu Cu-Al alloy

12 Complexities in X-ray production
Absorption

13 Complexities in X-ray production
Absorption

14 Complexities in X-ray production
Secondary Fluorescence

15 Complexities in X-ray production
Secondary Fluorescence 100 m From Milman-Barris et al. (2008)

16 Complexities in X-ray production
Quantitative analysis requires correction for production, absorption, and fluorescence effects Physics-based methods: ZAF, (z) Empirical method: Bence-Albee Correction depends on composition, which is not known a priori, so quantification is an iterative procedure Accurate analysis requires appropriate standards, as we will see when we learn electron probe analysis

17 EBSD

18 EBSD configuration

19 Diffraction: Bragg Equation
where n is an integer, λ is the wavelength of the electrons, d is the spacing of the diffracting planes, and θ is the angle of incidence of the electrons on the diffracting plane Constructive interference between reflections off successive planes of charge in the lattice requires difference in path length to be an integer multiple of the wavelength.

20 Aside: X-ray Diffraction
X-ray diffraction is usually done with a plane-wave X-ray source For monochromatic X-radiation and a single crystal, this gives a distribution of points of constructive interference around the sphere. For monochromatic X-radiation and a powdered material, this gives a set of single cones with opening angle 2 around the irradiation vector. For white incident X-ray source and powdered material, energy-dispersive detector at fixed 2 angle sees a set of discrete energy peaks

21 Aside: X-ray Diffraction
X-ray diffraction is usually done with a plane-wave X-ray source For monochromatic X-radiation and a single crystal, this gives a distribution of points of constructive interference around the sphere. For monochromatic X-radiation and a powdered material, this gives a set of single cones with opening angle 2 around the irradiation vector. For white incident X-ray source and powdered material, energy-dispersive detector at fixed 2 angle sees a set of discrete energy peaks

22 Aside: X-ray Diffraction
X-ray diffraction is usually done with a plane-wave X-ray source For monochromatic X-radiation and a single crystal, this gives a distribution of points of constructive interference around the sphere. For monochromatic X-radiation and a powdered material, this gives a set of single cones with opening angle 2 around the irradiation vector. For white incident X-ray source and powdered material, energy-dispersive detector at fixed 2 angle sees a set of discrete energy peaks So, for 10 keV, 1.24 angstroms

23 Kikuchi pattern formation
(Observed in TEM in 1928!) So, for 10 keV, angstroms

24 Kikuchi pattern formation
The monument to Kikuchi in Kumamoto (?)

25 Kikuchi pattern formation

26 Kikuchi pattern formation

27 Kikuchi pattern formation

28 Band detection 5 to 7 lines is usually enough for phase ID and orientation Hough Transform

29 Pattern indexing Good pattern match determines crystal structure and orientation

30 EBSD experiment modes Point analysis: phase and orientation determined at each analytical point

31 EBSD experiment modes Orientation mapping

32 EBSD experiment modes Grain mapping

33 EBSD experiment modes Texture

34 EBSD experiment modes Phase discrimination (automated point counting!)

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